Present sorting machines utilize one of two alternative schemes for determining a product's reflectivity, (either multichromatic or monochromatic). On the one hand an apparatus may attempt to measure only the light that is reflected from the product. Alternately, an apparatus may intentionally measure both the light reflected from the product and the light reflected from the background and then attempt to differentiate between the two.
The first scheme, attempting to measure only the light reflected from the product, is the more difficult of the two alternatives. Succeeding products in a product stream do not follow identical paths. Hence a viewing window may frame a view of a part of the product and a part of the background. Correcting this situation by making the viewing window small in relation to product size results in placing a limitation on the total surface of the product viewable. It might result in missing the product altogether due to variance in the product stream trajectory.
In the second scheme, a viewing window, or frame, is intentionally chosen that is wider than the product so that all (at least from one perspective) of the product will be viewed through one frame in successive instances. Each framed view of the product necessarily contains some view of the background. Typically a background is selected with the same reflectivity as the average good product. Any reflectivity measurement differing substantially from the acceptable background reflectivity is taken as an indication of an unacceptable product.
This second technique has limitations. Since products of different size fill the viewing frame to different degrees, products with equally unacceptable reflectivity characteristics will generate different measurements. The machine cannot discriminate between different sized products. Moreover, views of the same uniformly colored product from different perspectives will generate different estimates of product reflectivity if the product is of a shape to present different amounts of viewing area in different directions.
It is advantageous to be able to sort products based on their overall reflectivity, independent of their size and particular trajectory. It is also desirable to sort a wide variety of products without changing backgrounds. It is also desirable to estimate product size.
It is a feature of the present invention to provide for sorting in an improved manner based on both product reflectivity and frame fill information. The frame fill and the reflectivity are measured as the product passes a viewing frame, or frames, by an apparatus that is tolerant of product trajectory variations and viewing station background variations.